Combustion with fluidization and after-burning



y 7, 1964 J. 6. WILSON ETAL 3,139,726

COMBUSTION WITH FLUIDIZATION AND AFTER-BURNING Filed June 1, 1959 FIG. 2

INVENTORSZ JOSEPH G. WILSON ROBERT F. DUT'ITON TERRELL W. HAYMES JUSTIN C. DYGERT THEIR ATTORNEY United States Patent 3,139,726 COMBUSTION WITH FLUIDIZATION AND AFTER-BURNING Joseph G. Wilson, Riverside, C0nn., Robert F. Dutton, Hartsdale, N.Y., Terrell W. Haymes, Darien, Conn., and Justin C. Dygert, Walnut Creek, Calif., assignors to Shell Oil Company, a corporation of Delaware Filed June 1, 1959, Ser. No. 817,416 23 Claims. (Cl. (SO-39.02)

This is a continuation-in-part of our application Serial No. 747,008, filed July 7, 1958, now abandoned.

The invention relates to the combustion of fuel in a fluidized bed of finely-divided solids wherein the fuel is partly burned to produce exit gas which contains carbon dioxide and carbon monoxide together with entrained solids and is incapable of self-sustained normal combustion at the exit temperature when commingled with supplemental air. (The expression normal combustion is used to denote combustion without either heating, as by a flame which consumes supplemental fuel, or by contact with an oxidation-promoting catalyst.) The solids which are fluidized may, for example, be non-combustible or combustible bodies with which the fuel is combined naturally or artificially either prior to or during the combustion, e.g., metal oxide cracking catalyst bearing carbonaceous deposits which are burned, comrninuted coal or coke, or material which supplies oxygen for the combustion e. g., ore to be reduced.

More particularly, the invention relates to an improvement in such a combustion wherein energy is recovered from the said exit gas by expanding the exit gas in a turbine, subsequently further burning it in a boiler after adding supplemental air or oxygen-containing gas (for convenience hereinafter called supplemental air), and utilizing the shaft power generated by the turbine to drive a compressor which supplies at least the fluidizing gas and, preferably, also the supplemental air, whereby the plant can be self-powered.

Examples of applications are: (1) the burning of carbonaceous deposits on powdered contacting agents, particularly cracking catalyst consisting of metal oxides which were used in cracking hydrocarbon oils, to regenerate the contacting agent; (2). the burning of oil contained in oilbearing diatomaceous earth to produce light-weight aggregate; (3) the burning of fly ash which is produced when powdered coal is consumed in a furnace and which still contains oxidizable fuels; (4) the burning of ash which produced when shale oil is retorted, the said ash containing carbonaceous constituents; (5) the burning of limestone which is admixed with coal, soot or coke for the production of lime; (6) the burning of finely-subdivided coke; and (7). reduction of finely divided metal ores, such as iron ore, by a reducing agent, such as a hydrocarbon oil or combustible gas, e.g., methane. All but the last two examples involve the combustion of low-grade fuel; the lime constitutes the solid material, produced in situ, in the process in the fifth example; the fuel itself is the solid material in the sixth example; and in the last example the reducing agent is the fuel, which is oxidized by the ore. In all but the last example the oxidizing agent is contained in the fluidizing gas and in the last example the fuel constitutes or is a constituent of the fluidizing gas.

Such combustions as the foregoing can be effected in a fluidization chamber containing the solid particles through which a fluidizing gas is passed upwards at a rate to maintain the particles as a fluidized bed, i.e., in a turbulent state with quasi-liquid properties, including a recognizable upper level. Depending upon the system, the fluidizing gas may contain the oxidant and/ or the fuel. The fuel is partially burned to form gaseous combustion products which emerge from the top of the fluidized bed together 3,139,726 Patented July 7, 1964 with entrained solids and unreacted fluidizing gas, such as nitrogen or other inert gas. Because the fluidizing gas is usually air in cases wherein the oxidant is a gas it will, for brevity, be usually so called he ein, it being understood that the word is intended to have a generic connotation and that the invention is applicable also to the case wherein the fuel constitutes or is a part of the fluidizing gas.

Complete oxidation of such fuel to carbon dioxide in such a fluidized burning operation is usually not feasible. Incomplete combustion is often the result. of the use of only a limited amount of air to avoid excessive compression costs as well as to control the temperature in the fluidized bed. For example, in the regeneration of catalyst, such as silica-alumina particles, which was used in the cracking of hydrocarbons, the temperature in the fluidized bed must be sufliciently high to maintain combustion, e.g., above 650 F., but temperatures above 1050 F. to 1150 F. often cause deterioration of the catalyst. Higher temperatures are usually undesirable for the further reason that the gas emerging from the fluidized bed inherently entrains solid particles which must be separated not only to conserve the solids and avoid air pollution but also to prevent injury to the boiler and, in the present invention, to the blades of the turbine. Excessively high temperatures lead to rapid deterioration of cyclones and similar separators which are used to clean this gas. Complete combustion of the fuel in the fluidized bed is, moreover, often not possible with reasonable amounts of air because the exit gas is in equilibrium with freshly charged fuel in cases in which the process is carried out by continuously feeding the charge and discharging the solid particles.

Such fluidized combustion processes require large-volume streams of compressed fluidizing gas, which have heretofore been supplied by compressors consuming extraneous power. Although some of the sensible heat and fuel value of the exit gas has heretofore been recovered to produce steam, this has not been sufficient to meet the compression requirements but has involved continuing power consumption for compression.

It is the object of this invention to effect a saving in compression costs in carrying out such a combustion in a fluidized bed of solids by recovering a greater amount of energy from the exit gas by expanding the exit gas in the turbine of a turbine-compressor set which compresses sufficient gas to meet at least the fluidizing gas requirements of the process, adding supplemental air to the turbine exit gas and thereafter further burning the carbon monoxide in a boiler to generate steam or other vapor; preferably, the turbine-compressor set also provides the supplemental air.

A further object is to provide an improved integrated plant for carrying out a combustion in a fluidized bed of solids which includes a fluidization-combustion chamber for incomplete combustion of the fuel, an inertial separator. for removing entrained solids from exit gas without substantial drop in the gas temperature, an expansion turbine-compressor set which is operated on the clean exit gas from the separator and can meet the compression requirements of the plant, and a carbon monoxide boiler (also known as a waste-gas boiler) connected to receive the gas from the turbine exhaust. Ancillary objects are to provide an integrated plant which is economical in operating and capital costs; which uses simple controls; and which can be installed on a small plot area.

Additional objects will become apparent from the following description.

In summary, according to the invention, the mass of divided solids containing fuel and a fuel oxidant as reactants is confined in a fluidization-combustion chamber at a substantial superatmospheric pressure suflicient to permit expansion of exit gas therefrom in a turbine, and a fluidizing gas containing one of said reactants (fuel or oxygen) is passed upwards through the bed to fluidize the solids and effect partial combustion of the fuel with the production of combusted gas which contains carbon dioxide and carbon monoxide but is incapable of selfsustained, normal combustion at the exit temperature when admixed with supplemental air; the solids are, in most applications, supplied to and/ or removed from the chamber continuously or intermittently during the combustion; the said combusted gas emerges from the fluidized bed and is freed from entrained solids without materially lowering its temperature in an inertial type separator, preferably a series of cyclones; the resulting clean gas is passed through an expansion gas turbine which is coupled to a compressor wherein the fluidizing gas and supplemental air are compressed; and the turbine exit gas is mixed with the supplemental air and subjected in a carbon monoxide boiler to conditions causing further burning wherein the carbon monoxide is oxidized to carbon dioxide, either by heating with an auxiliary fuel burner and/or by contact with a catalyst, to transfer heat to the boiler tubes by radiation and convection. Because the boiler is usually operated at low pressure the supplemental air may be supplied from another source, e.g., by induction When a tall stack is used.

The invention will be described in detail with reference to the accompanying drawings forming a part of this specification andshowing diagrammatically, by way of illustration, a specific embodiment suitable for the regeneration of carbonized, finely divided catalyst, and a modification wherein:

FIGURE 1 is a front elevation of the apparatus, parts being broken away;

FIGURE 2 is an enlarged sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged fragmentary side elevation of the boiler; and

FIGURE 4 is a fragmentary sectional view of the lower part of the boiler, showing a modification wherein a catalyst is employed.

Referring to the drawings, the principal parts of the apparatus are: a vertically elongated fluidization-combustion chamber provided with a fluidizing air inlet pipe 11 connected to a bed air distributor 12, which is situated within the lower part of the chamber, and containing within the upper part a series of inertial-type separators 13; one or more, e.g., a pair of expansion gas turbines 14, 14a each having a direct-drive connection to a corresponding compressor 15 or 15a and a boiler having a boiler-housing 16 mounted on top of the fluidization chamber and containing an auxiliary fuel burner 17 and boiler tubes 18 connected to a steam drum 19.

It will be understood that although the drawings show only one turbine-compressor set 1415 for supplying fluidizing air and only one set 14a-15a for supplemental air, a plurality of sets may be employed for each purpose. The turbines and compressors may be mounted at the top of the fluidizing chamber, as shown.

The fluidization-combustion chamber 10, which has sufficient strength to confine gas under substantial superatmospheric pressure, such as 15 to 35 pounds per square inch gage, is mounted on a support structure 20 and has a frusto-conical bottom 21 which is open at the bottom and connected to a solids discharge pipe 22 fitted with a slide valve 23. A riser feed pipe 24 extends upwards through the bottom to receive the carbonized catalyst charge from a standpipe 25 and pressurized lift air is supplied, either from the pipe 11 or from an extraneous source, not shown, through a pipe 26. The feed pipe discharges against a deflector 27. The upper part of the chamber is enlarged as shown at 28 to accommodate the separators and has a top closure wall 29.

The inertial separators include a plurality, e.g. three stages of cyclones. It will be understood that any desired number, e.g., one to six, of cyclones may be used for each stage. Each first-stage cyclone 30 has an intake 31 positioned to receive gas above the top of the fluidized bed, indicated at L, a solids outlet pipe 32 which extends down into the fluidized bed in the form of a dipleg, and a gas outlet duct 33 which is connected to the intake of a second-stage cyclone 34. Each second-stage cyclone also has a solids outlet pipe 35 extending into the fluidized bed and a gas outlet pipe 36 which discharges into a distributing chamber 37 between the closure Wall 29 and a transverse partition 38. The central part 38a of this partition is upwardly convex or dished for structural reasons and supports a large number, e.g., ten to sixty, of small, third-stage cyclones having outer tubes 39 which extend through the partition. In the embodiment shown, each third-stage cyclone includes, further, a smaller, concentric gas outlet tube 40 which is fitted to a hole in the closure wall 29 and swirl vanes 41 in the annular space between the tubes. Solids, together with some bleed gas, are discharged at or near the bottoms of the tubes 39 through slits 42 which may be surrounded by skirts 43,

, into a collecting chamber 44 defined by a hopper 45;

the separated solids and bleed gas are discharged through a solids discharge duct 46 which extends out through the wall of the chamber 10.

The boiler housing has a floor plate 47 spaced above the closure wall 29 to define a plenum chamber 48 into which the clean gas is discharged from the third-stage cyclone tubes 40. This gas flows out through gas outlets 49 and 50 and ducts 51 and 51a to the turbines 14 and 14a, respectively. These gas ducts may have emergency shut-off valves 52 or 52a and nozzles 53 or 53a through which quench steam or water can be injected under control of valves 54 and 54a to maintain a safe temperature at the turbine intake. The latter valves may be operated automatically by a temperature controller as shown for the turbine 14a at 55, having a sensing element at the turbine intake and connected to valve operators 56 and 56a.

Suitable vent means are provided to vent the hot gas so as to limit the pressure Within the fluidization-combustion chamber and, thereby the power input to the turbines. Thus, there can be a single vent stack 57 (FIG- URE 3) connected to the chamber 48 and provided with a throttling vent valve 58. The vent valve is operated to vent gas as required; for example, it may be operated manually or by any of a variety of controls. In one specific arrangement, a pressure controller 59 having a pressure-sensing element in the chamber 48 is connected to a valve operator 60 to vent the amount of gas required to maintain a constant pressure in the chamber 48 and, hence in the fluidization chamber and at the turbine inlets.

The turbine exits are connected by ducts 61 and 61a to the bottom of the boiler housing. The lower part of the housing contains a refractory casing 62 which is joined to the boiler wall by an annular wall 62:: and extends upwards from the burner 17 to define an auxiliary combustion chamber. An auxiliary fuel, such as fuel gas, is supplied to the burner by a fuel pipe 63. The burner includes an air box 64 to which supplemental combustion air is supplied through an air pipe 65 from the compressor 15a in amount suflicient to burn the auxiliary fuel and the carbon monoxide in the turbine exit gas, which enters the combustion chamber as an annnular stream.

The boiler tubes 18 are connected at the bottom to a header 66 which is connected by an external pipe 67 to the steam drum 19. The upper ends of the tubes are connected to the steam drum through a header 68 and pipes 69. The upper part of the boiler may contain economizer tubes 70 for preheating feed water to the steam drum. Steam is discharged from the drum through a pipe 71. The boiler is open at the top and my be provided with a short stack 72.

Heat is also abstracted from the fluidized bed by means of a bed coil 73 which is mounted in the lower part of the chamber 10. Water from the steam drum is fed to this coil through a pipe 74 and a circulating pump 75, which can be operated at a variable speed, and steam flows to the drum through a pipe 76. In addition to generating steam, this coil serves to control the bed temperature.

The compressor 15 has the discharge thereof connected to the air inlet pipe 11 to. supply combustion and fluidization air to the bed air distributor 12 The pipe 11 has a vent 77, controlled by a valve 78, through which compressed air is vented as required to regulate the temperature within the fluidized-combustion chamber by limiting the rate of air admission. The vent valve 78 can be operated manually or automatically by and of a variety of controls. For example, the pipe 11 may be provided with a flow-measuring device 79 which is connected to a flow controller 80; the latter is adjustable to permit the desired rate of air-fiow and has its output connected to a valve operator 81. Any desired rate of air flow can thereby be maintained. A similar vent 82, vent valve 83, flowmeasuring element 84, flow controller 85, and valve operator 86 may be provided in the supplemental air pipe 65, to regulate the air-flow to the boiler.

The inlet pipe 11 is further provided with a valve 87 and a branch pipe 88, having a valve 89, for introducing air from an extraneous source during start-up. Similarly, the air pipe 65 may have a valve 90 and a branch pipe 91 with a valve 92 for initial supply of supplemental air. However, initial air can be obtained by running the turbines on steam during start-up.

The fluidization-combustion chamber is optionally provided with a plurality of nozzles 93 through which quench fluid, such as steam or water, can be injected into the upper part of the chamber from a supply pipe 94 under control of a valve 95 to check after-burning. It will be understood that the chamber will be provided with other control means such as means for indicating the height of the fluidized bed and the bed temperature and pressure; these instruments, being well known per se, are not shown.

In operation, as applied for example to the regeneration of carbonized cracking catalyst most of which passes a US. standard 100-mesh screen, the catalyst is admitted continuously through the riser pipe 24, using lift air from the pipe 26 in an amount of the order of 10% of the fluidizing air. The catalyst is fluidized by fluidizing air admitted through the pipe 11 and distributor 12; initially this air is admitted through the branch pipe 88, valve 87 being closed and valve 89 being open. The catalyst particles are fluidized to a level L. The fuel, in the form of carbonaceous deposits on the catalyst particles, is gasified by partial oxidation and the formation of carbon monoxide and carbon dioxide. Typically, the mol ratio of carbon dioxide to carbon monoxide is about 1:5 and the regenerator gas contains 5-10 mol percent of carbon monoxide, the remainder being inert gas which consists predominately of nitrogen and steam. Regenerated catalyst is discharged continuously through the pipe 22 and valve 23. The temperature within the chamber 10 is regulated by circulating water through the bed coil 73 at a rate determined by the pump 75 and also by controlling the amount of air admitted through the pipe 11. The conditions may, for example, be controlled so that the gas emerging from the top of the fluidized bed has a temperature of 1050 F. and a pressure of 23 pounds per square inch gage.

The gases emerging from the fluidized bed often contain small amounts of unconsumed oxygen. In the space above the bed, where the concentration of high heatcapacity solids is low there is a possibility of further reaction of this oxygen with the carbon monoxide, known as after-burning, which would result in an uncontrolled 6 temperature rise and damage, to the cyclones. This can be prevented by injecting quench fluid through the nozzles 93.

Coarse catalyst particles entrained by the gas from the bed are separated in the firstand second-stage cyclones 30 and 34 and returned to the bed through the diplegs 32 and 35 and gas, containing only very fine particles, at a temperature of 1050 F. and a pressure of 20 pounds per square inch gage, enter the distributing chamber 37. The gas flows thence through the third-stage cyclones 39-43, which remove catalyst fines to the extent required to prevent damage to the boiler and turbine blades. These fine particles are usually so small as to be useless in catalytic cracking and are discharged through the duct 46. Clean gas, still essentially at the stated temperature and a pressure of 18 pounds per square inch gage, are discharged through the tubes 40 into the plenum chamber 48.

The gas flows from the chamber 48 through the gas ducts 51 and 51a to drive the turbines 14 and 14a. The turbines, in turn, drive the compressors 15 and 15a to supply fluidization air and supplemental air. When the turbines are in operation the valve 87 is opened and the valve 89 is closed.

The turbine exit gases, at 800 F. and 2 pounds per square inch gage, flow through the ducts 61 and 61a to the boiler, wherein they are commingled with flame gases resulting from operation of the burner 17 and containing suflicient supplemental air to burn the carbon monoxide in the turbine exit gas. It will be understood that during the start-up period supplemental air may be admitted to the burner through the branch pipe 91; alternatively, the burner may be placed into operation only after the turbines and compressors are working. The resulting mixture of gases has too low a calorific value for self-sustained normal combustion at the prevailing pressure and temperature. To eflect burning its temperature is raised by the burner 17 to 1400 F. to 1650 F., to create oxidizing conditions, at which the carbon monoxide is burned by self-sustained combustion. Flame or radiant gas emanating from the casing 64 imparts heat to the boiler tubes by radiation and convection. The combustion products then flow in heat exchange with the economizer tubes 70 and are discharged into the stack 72 at a temperature of 400 F. and atmospheric pressure.

It will be also understood that whilespecific temperatures and pressures were given to describe a particular embodiment in detail, these conditions are not restrictive of the invention.

The plant is controlled principally as follows:

(a) The turbines run unthrottled, at full capacity, driving the compressors at constant load to compress air at a constant rate.

(b) Excess compressed air is vented to the atmosphere through the vents 77 and 82.

(c) The pressure in the chamber 10 is: controlled by venting excess combustion gas to the atmosphere through the vent stack 57.

Further controls include the admission of cooling fluid through the nozzles 53 and 53a into the gas streams to the turbines to prevent excessive temperatures, e.g., to hold the gas temperature below 1100 F. to 1250 F.; the admission of quench fluid through the nozzles 93 into the top of the fluidization chamber to check after-burning; and the cooling of the bed by the bed coil 73.

Features of the invention, some of which are optional, are:

The boiler drum 19 serves also as a drum for the bed coil 73. This reduces the cost involved in the provision of a separate drum for the bed coils.

By locating the boiler on top of the fluidization chamber the need for a long gas duct between the fluidizationcombustion chamber and the boiler is eliminated; also eliminated are the need for a boiler stack and the separate plot area for the boiler.

. 7 Location of the small, last-stage cyclones inside the fluidization combustion chamber effects a reduction in installation costs resulting from elimination of piping, valves and separate vessels to contain the cyclone, in addition to reducing pressure and heat losses. I It is evident that the use of expansion gas turbine-compressor sets to provide air for the fluidization-combustion chamber and the boiler effects a reduction in the installed costs resulting from the use of simple and inexpensive turbine-compressors and a reduction in operating costs resulting from recovery of power formerly vented to the atmosphere.

By locating the turbines and compressors on top of the fluidization-combustion chamber there is a reduction in costs due to the elimination of a turbine-compressor building and the plot area required for such a building.

It will be understood that when the invention is applied to ore reduction the compressor 15 is used to compress a fuel-containing gas, such as methane or a mixture thereof with an inert gas, and that the vent 77, if used, would usually be connected to the source reservoir or other suitable receptacle instead of being vented to the atmosphere. 1

In the modification shown in FIGURE 4, the auxiliary fuel burner may be omitted. The turbine exit gas passes entering the combustion chamber 62a through a series of catalyst grids 96 and 97, which are coated with platinum or other suitable oxidation-promoting catalyst for effecting combustion. The supplemental air from the pipe 65 is mixed With the turbine exit gas by distributor pipes 98 and 99, each having a flow-control valve 100 or 101. The further burning induced by the catalyst produces hot combustion gas which heats the boiler tubes by radiation and convection as previously described.

We claim as our invention:

1. In the process which comprises the incomplete combustion of fuel within a closed fluidization-combustion zone containing a bed of finely-divided solid particles maintained in the fluidized state by flowing upwardly therethrough a fluidizing gas which contains a combustion reactant, wherein there is discharged from said bed an exit gas which contains entrained solid particles, carbon dioxide and carbon monoxide and is incapable of self-sustained normal combustion at the exit temperature when mixed with supplemental air, the improvement of recovering heat and Work energy from said exit gas sulficient to supply the said fluidizing gas by: maintaining said fluidization-combustion zone at a substantial superatmospheric pressure sufiicient to permit expansion of the exit gas in a gas turbine, substantially separating said entrained particles from the exit gas by inertia without substantially lowering the exit gas temperature, expanding the resulting clean gas substantially at the said exit temperature in expansion gas turbine means and thereby generating shaft power, discharging the clean gas from the turbine means at reduced pressure and mixing the turbine exhaust gas with supplemental air, subjecting the resulting mixture to oxidizing conditions within a boiler having fluid-confining heat-transfer walls to cause further combustion with oxidation of carbon monoxide and thereby heating said heat-transfer Walls by radiation and convection, compressing said fluidizing gas to said superatmospheric pressure by using said shaft power, and admitting the compressed gas into said fluidization-combustion zone.

2. Method according to claim 1 wherein said supplemental air is also supplied by compressing it by using said shaft power from said turbine means.

3. Process according to claim 2 wherein said fluidizing gas and supplemental air are compressed separately to different pressures, the fluidizing gas to the higher pressure and the supplemental air to the lower pressure.

4. Process according to claim 1 wherein said turbine means is operated at substantially constant power output by venting a variable amount of the exit gas after the separation of entrained solids therefrom and prior to expansion in the turbine means.

5. Process according to claim 4 wherein said fluidizing gas is compressed at a rate in excess of the influx to the fluidization-combustion zone, and the compressed gas is admitted into said zone at a desired rate by venting a controlled amount thereof.

6. Process according to claim 1 wherein said fluidizing gas is compressed at a rate in excess of the influx to the fluidization-combustion chamber, and the compressed gas is admitted into said zone at a desired rate by venting a variable amount thereof.

7. Process according to claim 1 wherein said step of subjecting the mixture to oxidizing conditions includes burning auxiliary fuel with a portion of said supplemental air and mixing the resulting hot combustion products with the said turbine exhaust gas and supplemental air to bring the said mixture to oxidizing temperature.

8. Process according to claim 1 wherein said step of subjecting the mixture to oxidizing conditions includes flowing said mixture of turbine exhaust gas and supplemental air in contact with an oxidation catalyst.

9. Process for regenerating spent finely divided metal oxide catalyst bearing carbonaceous deposits which comprises the steps defined in claim 1, wherein the solid particles in the fluidizing-combustion zone are the aforesaid catalyst particles, the fuel is the carbonaceous deposits on said catalyst particles, and said fluidizing gas is air.

10. In the process of regenerating spent finely divided metal oxide cracking catalyst bearing carbonaceous deposits, wherein said spent catalyst is continuously admitted into a closed fluidization-combustion zone, fluidizingcombustion air is continuously flowed upwardly through said catalyst to form a fluidized bed, said carbonaceous deposits are burned to produce an exit gas which is discharged from the top of said bed and contains entrained catalyst, carbon dioxide and carbon monoxide, said exit gas being incapable of self-sustained normal combustion at the exit temperature when mixed with supplemental air, and regenerated catalyst is continuously discharged from said zone, the improvement of recovering heat and work energy from said exit gas suflicient to supply the combustion and fluidization air requirements of the process by: maintaining said fluidization-combustion zone at a substantial superatmospheric pressure sufficient to permit expansion of the exit gas in a turbine, substantially separating said entrained catalyst from the exit gas by inertia without substantially lowering the exit gas temperature, expanding the resulting clean gas substantially at the said exit temperature in expansion gas turbine means and thereby generating shaft power, discharging the clean gas from the turbine at reduced pressure and mixing the turbine exit gas with supplemental air, subjecting the resulting mixture to oxidizing conditions within a boiler having fluid-containing heat-transfer walls to cause further combustion with oxidation of carbon monoxide, compressing the said fluidized-combustion air to said superatmospheric pressure by using said shaft power, and supplying the compressed air to the fluidization-combustion zone.

11. An integrated plant for the continuous combustion of fuel which comprises: a vertically elongated fluidization-combustion chamber adapted to confine gas at a substantial superatmospheric pressure sufiicient to permit expansion of said gas in a turbine; means for admitting finely-divided solids and one combustion reactant to said chamber; first gas inlet means for admitting a fluidizing gas and the other combustion reactant under said super atmospheric pressure into a lower part of the chamber at a controlled rate for fluidizing said solids and eifecting incomplete combustion to produce an exit gas at the top of the fluidized bed which contains entrained solids, carbon dioxide and carbon monoxide and is incapable of self-sustained normal combustion at the exit temperature rator connected to receive exit gas from said chamber for separating entrained solids therefrom without substantial lowering of the temperature; gas expansion turbine means having the intake thereof connected to receive clean gas from the separator substantially at the temperature at which said gas is discharged from said bed; a boiler including a housing and boiler tubes, said housing being connected to receive exhaust gas from said turbine means; second inlet means for supplying supplemental air to the turbine exhaust gas; means for subjecting the resulting mixture of turbine exhaust gas and supplemental air to oxidizing conditions in the boiler to effect combustion of the carbon monoxide; and compressor means drivingly connected to said turbine means and having the discharge thereof connected to said first gas inlet means so as to supply the fluidizing gas.

12. A plant according to claim 11 wherein said compressor means is connected also to said second inlet means so as to supply the supplemental air.

13. A plant according to claim 12 wherein said turbine means and compressor means comprises two turbines, a high-pressure compressor drivingly connected to one of said turbine and connected to said first gas inlet, and a low-pressure compressor drivingly connected to the other turbine and connected to said second inlet means.

14. In combination with the plant according to claim 11, a vent for discharging clean exit gas flowing before entry into said turbine means, and flow-control means for controlling the discharge of gas through said vent so as to regulate the pressure within the fluidization-combustion chamber.

15. In combination with the plant according to claim 11, a vent for the compressed fluidizing gas in the connection between the compressor means and the said first gas inlet means, and flow-control means for controlling the discharge of gas through said vent so as to regulate the rate of admission of fluidizing gas into said chamber.

16. A plant according to claim 11 wherein said means for subjecting the mixture in the boiler to oxidizing conditions includes an auxiliary fuel burner having an inlet for supplemental fuel and disposed to admix hot combustion products therefrom with the said mixture to heat the latter to oxidizing temperature.

17. A plant according to claim 11 wherein said means for subjecting the mixturein the boiler to oxidizing conditions includes an oxidation catalyst and a flow passageway for passing said mixture in contact with the catalyst.

18. A plant according to claim 11 wherein said turbine means is mounted above the fluidization-combustion chamber.

19. A plant according to claim 18 wherein said compressor means and boiler housing are mounted above the fluidization-combustion chamber adjacent to the turbine means.

20. Process for recovering energy from hot combustion gas under superatmospheric pressure, said gas containing carbon dioxide and carbon monoxide and being incapable of self-sustained normal combustion at the temperature thereof when mixed with supplemental air which comprises the steps of expanding the said gas in an expansion turbine and thereby generating shaft power; discharging said gas from said turbine at reduced pressure; mixing said discharged gas with supplemental air; and subjecting the resulting mixture to oxidizing conditions within a boiler having fluid-confining heat-transfer walls to cause further combustion with oxidation of carbon monoxide and thereby heating said heat-transfer walls by radiation and convection.

21. Process according to claim 20 wherein the said step of subjecting the mixture to oxidizing conditions includes burning auxiliary fuel with a portion of said supplemental air and mixing the resulting hot combustion products with the said turbine exhaust gas and supplemental air to bring the said mixture to oxidizing temperature.

22. In a plant for deriving energy from hot combustion gas having a substantial superatmospheric pressure, said gas containing carbon dioxide and carbon monoxide and being incapable of self-sustained normal combustion at the temperature thereof when mixed with supplemental air, which comprises: a source for said gas; a gas expansion turbine having the intake thereof connected to said source; a boiler including a housing and boiler tubes, said housing being connected to receive exhaust gas from said turbine; means for supplying supplemental air to the turbine exhaust gas; and means for subjecting the resulting mixture to oxidizing conditions in the boiler to effect combustion of the carbon monoxide.

23. Apparatus according to claim 22 wherein said means for subjecting the mixture to oxidizing conditions includes an auxiliary fuel burner having an inlet for supplemental fuel and disposed to admix hot combustion products therefrom with the said mixture to heat the latter to oxidizing temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,052,588 Janicki Feb. 11, 1913 1,263,390 Edwin Apr. 23, 1918 2,384,356 Tyson Sept. 4, 1945 2,432,177 Sedille Dec. 9 1947 2,559,623 {Holmes July 10, 1951 2,592,749 Sedille ct al. Apr. 15, 1952 2,605,610 Hermitte et al. Aug. 5, 1952 2,718,754 Lewis et a1 Sept. 27, 1955 2,853,455 Campbell et al Sept. 23, 1958 2,895,294 Terrell July 21, 1959 FOREIGN PATENTS 675,583 Great Britain July 16, 1952 

1. IN THE PROCESS WHICH COMPRISES THE INCOMPLETE COMBUSTION OF FUEL WITHIN A CLOSED FUIDIZATION-COMBUSTION ZONE CONTAINING A BED OF FINELY-DIVIDED SOLID PARTICLES MAINTAINED IN THE FLUIDIZED STATE BY FLOWING UPWARDLY THERETHROUGH A FLUIDIZING GAS WHICH CONTAINS A COMBUSTION REACTANT, WHEREIN THERE IS DISCHARGED FROM SAID BED AN EXIT GAS WHICH CONTAINS ENTRAINED SOLID PARTICLES, CARBON DIOXIDE AND CARBON MONOXIDE AND IS INCAPABLE OF SELF-SUSTAINED NORMAL COMBUSTION AT THE EXIT TEMEPERATURE WHEN MIXED WITH SUPPLEMENTAL AIR, THE IMPROVEMENT OF RECOVERING HEAT AND WORK ENERGY FROM SAID EXIT GAS SUFFICIENT TO SUPPLY THE SAID FLUIDIZING GAS BY: MAINTAINING SAID FLUIDIZATION-COMBUSTION ZONE AT A SUBSTANTIAL SUPERATMOSPHERIC PRESSURE SUFFICIENT TO PERMIT EXPANSION OF THE EXIT GAS IN A GAS TURBINE, SUBSTANTIALLY SEPARATING SAID ENTRAINED PARTICLES FROM THE EXIT GAS BY INTERIA WITHOUT SUBSTANTIALLY LOWERING THE EXIT GAS TEMPERATUE, EXPANDING THE RESULTING CLEAN GAS SUBSTANTIALLY AT THE SAID EXIT TEMPERATURE IN EXPANSION GAS TUBRINE MEANS AND THEREBY GENERATING SHAFT POWER, DISCHARGING THE CLEAN GAS FROM THE TURBINE MEANS AT REDUCED PRESSURE AND MIXING THE TUBINE 